Why would I need to purchase the box? Do you not get charged when you ship it, not beforehand? Way to deviate from the norm Canada Post.

It's a good deal, better than the regular services.

I sold a heavy textbook on eBay, wrapped it up in brown paper, and used Canada Post's website to calculate the postage rate. It was about $16. I put actual stamps on it and took it to the post office to mail it. The agent confirmed that I had put on the correct postage, but told me that a better deal would have been to buy the prepaid box for $13.49. Lower postage and a free box, what's not to like.

Just shipped something using the box, bought it from Richmond Hill post office, they seem to have stack of boxes for you to just grab and mail. It was super easy. But the lady behind the counter told me that it could take 1-3 business days to reach Mississauga, even though on the website it says Local is 1 business day. They do not guarantee it, while in express post they do. I totally forgot about the 5% discount...oh well, was in rush to send it out, hoping it reaches by Monday. Thanks for the post OP, perfect timing for me.

But I can't seem to find the locations any in have a link to the locations

same here, looked online
went back to op original post and there is a pdf file of locations ( maybe older)
but worked for me (OAKVILLE ONTARIO)
oakville hasty mart has them at the cp location at the back